In the art of motor vehicle speed regulators or cruise controls as they are often referred to, it is common practice to compare a vehicle speed signal with a predetermined, or set speed, signal to provide a control signal for operating an actuator connected to the vehicle throttle. One technique, known in the art is that of providing a rotating flyweight speed sensor to control the position of a vacuum valve in response to changes in vehicle speed. In vehicle speed regulators using this technique, the vacuum valve controls the vacuum in a chamber, and the chamber vacuum is then applied to an actuator bellows or diaphragm, motion of which is translated through intermediate linkages to the vehicle throttle. As the vacuum valve moves in response to movement of the flyweight speed sensor, the chamber vacuum is varied to cause differing amounts of movement to the diaphragm actuator. When the vehicle speed regulator of this type system is not in use, the flyweight governor is not actively coupled to the vacuum control valve. Upon activation of the system by the vehicle operator, the flyweight governor is clutched, for example, electrically to the vacuum control valve to thereafter control movement of the control valve in a manner proportional to the movement of the flyweight governor. The flyweight governor is usually driven by the vehicle speedometer cable drive. An example of this type of speed control system is set forth in U.S. Pat. No. 3,298,482.
Systems of the above-described type rely upon the mechanical motion of the flyweight sensor to provide the vehicle speed signal input. The flyweight sensor typically requires a rotary mechanical connection to the vehicle wheel; for example, to the transmission driven speedometer drive cable. In order to eliminate this rotary mechanical connection, it has been desired to produce an all-electrical speed regulator.
It is known in the art to provide an electrical speed regulator where the vehicle speed signal is provided by a wheel driven tachometer generator, attached, for example, to the vehicle drive train or transmission. The signal from the tachometer generator is then electrically compared with a signal corresponding to the desired operator selected set speed. The comparison of these electrical speed signals is then used to drive a servomotor for moving the vehicle throttle in a manner so as to maintain the vehicle speed within a desired degree of agreement with the operator selected set speed.
With either of the above-described systems for controlling vehicle speed the throttle actuator, connected to the vehicle throttle, is caused to move the throttle by an amount proportional to the control signal which moves in accordance with the difference between the vehicle speed and the desired speed. Such an arrangement tends to cause the vehicle to change speed too rapidly in response to a large throttle change, and thus causes the vehicle to overshoot the set speed and create a difference in the opposite sense. For example, if the system calls for a great increase in throttle opening in response to a large difference between vehicle speed and set speed, drastic acceleration of the vehicle may cause the vehicle to increase in speed well above the set speed before the system can change the control signal for varying the throttle position. Thus, it has been found necessary to provide some means of modifying the control signal or its effects to prevent the vehicle from "hunting" or oscillating about the set speed. One technique which has been used is set forth in U.S. Pat. No. 3,298,482, mentioned above, where the position of the throttle is applied by feedback means to change the bias on the valve member in a manner so as to counteract the efforts of the flyweight governor to move the valve member to produce a greater vacuum in the chamber for controlling the actuator. Another technique which has also been used, is described in U.S. Pat. No. 3,575,256, wherein the throttle position is sensed by a transducer providing an electrical signal, which electrical signal is applied to electrical means comparing vehicle speed with set speed for producing the control signal. In this type speed regulator the position of the throttle affects the electrical control signal applied to the servoactuator.
Where it has been found desirable to provide a vehicle speed control having all electrical means for sensing and comparing speed signals and for providing a control signal, it has been found extremely difficult to duplicate the throttle position feedback attenuating feature provided in the all-mechanical system. Although the above-described electrical system provides a throttle position feedback signal, it is used to modify the electric control signal to the servoactuator. Unfortunately, providing feedback modification or attenuation to the control signal generator for the servoactuator does not insure linear response of the combination of servoactuator and vehicle engine throttle, and therefore oscillation about the set speed occurs.
In the construction of the conventional vehicle throttle, the carburetor throttle mechanism has nonlinear return biasing, with respect to motion of the throttle actuating linkage, in order to give a linear throttle-power response from the engine. A servoactuator operating against nonlinear throttle actuator systems and which attempts to apply a linearly controlled response force to the throttle, produces the overall nonlinear vehicle response known as "hunting" wherein the vehicle speed is caused to oscillate about the set speed. In order to minimize the characteristic of the system known as "hunting", it has been found necessary to provide some means of directly damping or attenuating the movement of the throttle servoactuator as the vehicle approaches the set speed.